This invention relates to new and useful improvements in drilling, particularly in drilling in rock formations.
Conventionally, a drill bit is situated at the bottom end of a drill string and rotation is supplied to the entire drill string and drill bit from the ground surface. Pressure is applied to the drill bit not only by the weight of the drill string but also by additional weight such as that applied by weight collars around the string just above the drill bit at the bottom of the hole.
This conventional method requires considerable weight and is relatively slow in operation and, if downward pressure is applied mechanically, considerable mechanism is required.
Furthermore, the drill string is basically suspended from the rig in order to prevent buckling of the drill string due to the static weight thereof.
Devices exist which eliminate the heavy collars used to increase the downward force exerted upon a drill bit, and which use hydraulic pressure to force a section of the drill string above the drill bit into contact with the sides of the drill hole. All of these require that the portion of the string or pipe in contact with the hole remain stationary, while some other device is used to push against this part of the drill string thus exerting a downward force upon the drill bit.
However, these devices require a totally different method of operation for the drill bit and cannot be adapted for use with conventional, rotatable drill strings.